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With the increasing installation of the high-voltage direct current device and flexible AC transmission system, the power transfer capability increases significantly. However, the risk of line overloads or even cascading failures caused by DC blocking or line outage also augments, which requires accurate and effective post-contingency corrective control (CC) actions. Traditional sensitivity-based methods are fast, but are less accurate and may suffer from the seesaw problem. Artificial intelligence optimisation-based methods usually exhibit better CC performance but are time-consuming. For fastly performing accurate CC actions, a second-order cone programming (SOCP)-based CC optimisation model for line overloads alleviation in meshed AC/DC power systems is proposed. Initially, to reduce the number of CC actions and optimisation variables (OVs), a heuristic search method is proposed to automatically select the most effective generators/loads for the overloaded lines. Subsequently, thyristor controlled series capacitor (TCSC) compensation levels and multi-terminal direct current (MTDC) power are treated as additional OVs to minimise load shedding/generation rescheduling. Additionally, to boost computational efficiency, SOCP format power flow equations for systems with MTDCs and TCSCs are proposed. Eventually, the effectiveness, accuracy, and superiority in computational efficiency of the proposed method are verified based on the modified IEEE 30-bus test system.

Accurate detection and effective control strategy of commutation failure (CF) of high voltage direct current (HVDC) are of great significance for keeping the safe and stable operations of the hybrid power grid. At first, a novel detection method for consecutive CF is proposed. Concretely, the 2nd and higher orders’ derivative values of direct current are summarized as the core to judge CF by analyzing the physical characteristics of the direct current waveform of the converter station in CF. Then, the Daubechies wavelet coefficient that can represent the 2nd and higher order derivative values of direct current is derived. Once the wavelet coefficients of the sampling points are detected to exceed the threshold, the occurrence of CF is confirmed. Furthermore, by instantly increasing advanced firing angle β in the inverter side, an additional emergency control strategy to prevent subsequent CF is proposed. Eventually, with simulations of the benchmark model, the effectiveness and superiorities of the proposed detection method and additional control strategy in accuracy and rapidity are verified.

With the aid of power quality monitoring systems (PQMSs), accurate locating of voltage sag sources, which has important significance for guiding maintenance personnel in finding and repairing faults as well as improving power supply reliability, has been becoming a new research hotspot. However, existing methods have unsatisfactory locating accuracy due to the integration of distributed generators (DGs) and fault resistance. In this paper, a novel strategy for accurately locating voltage sag sources in smart distribution networks is proposed. Based on inverse theory, which is well applied in geophysics, the accurate location issue is treated as a two-step optimization model. It aims at making the distribution of voltage phasors and current phasors obtained by theoretical short-circuit calculation match those actually observed as closely as possible. To guarantee the feasibility of the strategy, the effect of inverter-interfaced DGs (IIDGs) which are the main form of DG is considered in the short-circuit calculations. To guarantee the location accuracy of the strategy, fault resistance is treated as an optimization variable in the two-step optimization model to eliminate estimation error of fault resistance. Via two modified IEEE benchmarks with different scales, the validity and the superiorities in applicability and accuracy of the proposed strategy are verified.

Accurate locating and capacity assessment of capacitor switching can be used to verify whether the instruction of capacitor switching from distribution automation (DA) master station is correctly carried out. In this paper, a novel locating strategy, which can obtain the accurate locations as well as capacities of simultaneously switched capacitors at different places in distribution network, is proposed. Firstly, the steady state and perturbation transient information collected by power quality monitoring system (PQMS) is synthetically analyzed to judge whether the disturbance is caused by capacitor switching. And, the indices of regional net increments of reactive and active power, which can distinguish the mutual influence between switched capacitors in different regions, are proposed to determine the candidate area in DA master station. Further, based on inversion match of power flow, an optimization model is developed to realize precise locating and capacity assessment. Eventually, via the IEEE 33-node benchmark, the effectiveness and superiorities of the proposed strategy are verified.

Isolated grid (IG) usually has small inertia constant, and the primary frequency regulation ability of IG is limited. In addition, high penetration level of photovoltaic power plants (PV-PPS)integrated to IG deteriorate system inertial and primary frequency regulation ability. To ensure the stability of frequency, UC model considering dynamic frequency limit (DFL) is proposed in this paper, and PV-PPS are deloaded to participate in frequency regulation. Based on frequency response model with PV-PPS participating in frequency regulation, the expression of required minimum frequency regulation capacity of PV-PPS is deduced, which guides PV-PPS retain sufficient but not excessive capacity. Then, a UC model with DFL and frequency regulation capacity of PV-PPS constraints is proposed. And the problem is decomposed into a master problem for UC with DFL and a subproblem for PV-PPS' frequency regulation capacity assessment. Because the master problem is a complex nonlinear mixed integer optimization problem, in order to avoid complexity solving procedure, unit regulation power is used to present frequency regulation ability and generate optimization cut. The optimization cut and benders cut are used for eliminating frequency limit/regulation capacity violations in iteration method. Finally, an IG test system is used to verify the effectiveness and advantages of the proposed scheme, comparing with other two schemes: conventional UC and UC considering DFL without PV-PPS participating in frequency regulation.

Active power steady-state security regions (APSSRs), which can provide guidance for prevention and control through security checks, is of great importance for the safe operation of power systems in which more and more sustainable energy power generation is integrated. As a mature flexible AC transmission system (FACTS) device, thyristor-controlled series compensators (TCSCs) can carry out series compensation for the transmission line by controlling its equivalent reactance. With the change of the equivalent reactance parameter of a TCSC, the nodal admittance matrix and power flow distribution of the power system also changes. Inevitably, the APSSR will be different. Therefore, it is necessary and important to further incorporate the equivalent reactance parameters of TCSCs in the APSSR expression, which is generally established in the space of node active power injections. In this paper, a rapid construction method of APSSRs incorporating the equivalent reactances of TCSCs is proposed. Firstly, applicability and efficiency of the conventional APSSR construction method for power systems with TCSCs are analyzed. Further, with equivalent disconnection of TCSC branches, the effect of TCSC equivalent reactances on the distribution of active power flow through changing the structure parameters is treated as modifying node active power injections. On this basis, explicit expressions of APSSRs with a single TCSC equivalent reactance parameter and double TCSC equivalent reactance parameters are derived, respectively. Moreover, by deducing the general formula of APSSRs with multiple TCSC equivalent reactance parameters, the feasibility of the proposed method for power systems with multiple TCSCs is analyzed. Eventually, via benchmarks with different scales and a different number of TCSCs, validity and superiorities of the proposed method in computational efficiency are demonstrated.

Harmonic resonance may cause abnormal operation and even damage of power facilities, further threatening normal and safe operation of power systems. For renewable energy generations, controlled loads and parallel reactive power compensating equipment, their operating statuses can vary frequently. Therefore, the parameters of equivalent fundamental and harmonic admittance/impedance of these components exist in uncertainty, which will change the elements and eigenvalues of harmonic network admittance matrix. Consequently, harmonic resonance in power grid is becoming increasingly more complex. Hence, intense research about prevention and suppression of harmonic resonance, particularly the parameter feasible domain (PFD) which can keep away from harmonic resonance, are needed. For rapid online evaluation of PFD, a novel method without time-consuming pointwise precise eigenvalue computations is proposed. By analyzing the singularity of harmonic network admittance matrix, the explicit sufficient condition that the matrix elements should meet to prevent harmonic resonance is derived by the extended Gersgorin theorem. Further, via the non-uniqueness of similar transformation matrix (STM), a strategy to determine the appropriate STM is proposed to minimize the conservation of the obtained PFD. Eventually, the availability and advantages in computation efficiency and conservation of the method, are demonstrated through four different scale benchmarks.